Experiments were conducted on cats to study the pharmacokinetics of polyosm possessing diuretic and antiedemic properties whose primary acting component is polyethyleneoxide 400. Biexponential dependence of the blood drug concentration on the time with T1/2 values of 41 min and 4.8 h was revealed. In the first 5 h after intravenous infusion of the drug 60.8% of the introduced dose of polyethyleneoxide 400 (1 g/kg) was excreted through the kidneys.